“Too Cute. Too Cute. Moon Yadda.”
“This is Too Cute.”
Pause.
“Too Cute. Too Cute. Moon Yadda.”
“Moon Yadda, Moon Yadda, this is Too Cute.”
Pause.
“Too Cute. Too Cute. Moon Yadda.”
“Moon Yadda, Moon Yadda, Moon Yadda, this is Too Cute. This is Too Cute.”
Long pause.
“MOON YADDA, MOON YADDA, MOON YADDA.”
Tip #1: Shouting into the microphone doesn’t help. When you can hear all the other boats on VHF and they cannot hear you unless you are in the same harbor, odds are that there is something wrong with your radio installation. It could be the radio, particularly if you didn’t do your homework before you bought it. However, if you have a name-brand radio and it is delivering substandard performance, odds are that the problem is with the installation rather than the radio.
Big Wire The most common cause of limited transmit range is power supply wiring of inadequate size. Don’t be mislead by the supply wire furnished with the radio. This short power lead is intended to connect to a proximate terminal block or some other full-voltage power source within inches of the radio. The voltage drop over a short length of this small-gauge wire will not be significant, but you cannot extend the power lead with the same size wire and run it 20 feet away to your breaker panel or battery bank. If you do, you will cripple the transmit range of your radio.
Virtually all fixed-mount VHF radios are rated at 25 watts output on the high-power setting. This, however, is actually the legal limit on this type of radio. True output, even under optimal conditions, can be as much as 20 percent less. Because VHF range is limited to
line of sight plus 22 percent (the signal bends slightly over the horizon), even 20 watts of output power would normally be sufficient.
But you only get those20 watts if you are feeding the radio around 13.8 volts—the battery voltage that we might expect with the engine running. Reducing the supply voltage to the radio has a direct effect on transmitter output. You should expect to lose close to five watts of transmission power for ever one-volt reduction. So with the engine off and the batteries at full charge voltage of 12.65, a 20-watt radio puts out closer to 15 watts. Let the battery voltage decline below 12 volts and the transmission output drops close to 10 watts—just twice the output of a
handheld radio.
Add some resistance in the supply wiring and the voltage at the radio drops even lower. So does your transmit range. If your radio is wired with 16 AWG wire, (unfortunately not that unusual) and the round-trip wire distance to the breaker panel is 50 feet, the voltage at the radio during transmission will be more than a volt lower than your battery voltage. With a partially depleted house bank, you will get better performance from two Dixie cups and a long string.
So what size should the supply wire be? Not smaller than 12 AWG. If the round-trip wire-run distance to the breaker panel is greater than 30 feet, you should use 10 AWG wire. Also make sure that the cable from the battery to the breaker panel is of sufficient size to deliver full battery voltage with all panel circuits drawing their anticipated currents.
Big Coax A full 25 watts of output from your VHF radio doesn’t get you a thing unless you can deliver it to the antenna. If you scrimp on the size of the coaxial cable connecting radio and antenna, you reduce the performance of even the best radio. A 50-foot run of RG-58 coaxial cable cuts your output at the antenna by more than half. If your radio is putting out a full 25 watts, the effective output at the masthead will be around 12 watts. But installation deficiencies are cumulative. For example, if your output at the radio is only 15 watts due to depleted batteries or too-small supply wiring, expect your masthead output with RG-58 cable to be around seven watts.
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| "There is simply no place on a sailboat where RG-58 coaxial cable is a good choice. " |
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If you don’t know what size coax connects your radio to your antenna, shame on you. Go look. It should be printed on the outside of the cable. There is simply no place on a sailboat where RG-58 coaxial cable is a good choice.
Some cheap antennas come with RG-58 attached. Leave these to the powerboaters, who have short cable runs and generally have the engine running when the radio is in use. For a sailboat operating on stored energy and transmitting through an antenna 50 or 100 feet from the radio, the absolute minimum is RG-8/U coax. Do not confuse this with RG-8/X, which is about half the diameter of RG-8/U. Using RG-8/X—sometimes called mini 8—will nearly double the signal loss when compared to RG-8/U.
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A better choice than RG-8/U is RG-213/U. These two cables are identical in size and very close in signal loss, but the RG-213/U has a better jacket. Water intrusion is a problem with coaxial cable, and unless the jacket carries a “noncontaminating” designation—which RG-213/U does—moisture eventually penetrates, sometimes sooner rather than later. Because the radio signal travels not through the wire but on its surface—in this case on the outside surface of the core conductor and on the inside surface of the braided shield—surface corrosion that occurs as a result of moisture intrusion has an immediate detrimental effect on signal strength at the antenna. If your radio once delivered sparkling performance, but now it doesn’t seem to get out as far, suspect corrosion inside the coax. Even coax with noncontaminating jacket can admit water at the ends if the cable connectors are not perfectly sealed.
There are other coaxial cable choices, but be very careful. Never use TV coax, not even the huge stuff used for cable transmission. A VHF radio requires coax with an impedance of around 50 ohms and TV coax has a 72 to 75 ohm impedance.
Ham operators face the same problems with signal loss, so there are some very good, very big 50-ohm coaxial cables available that can reduce signal loss even more. But for the marine environment, cables with foam or air dielectric (the element separating the core and the braid) bring a higher risk of shorter cable life because they will allow moisture to wick through the cable. A solid or at least closed-cell dielectric is better. Unless you have expert advice you trust, stick with RG-213/U.
Soldered terminals On final weak link is the end connectors. The connectors at both ends of the cable should be soldered to the cable. Solder connectors are not difficult to do, but if you don’t feel competent to attempt this, do not fall back on crimp connectors as your alternative. Find a hobbyist friend or pay a technician to attach proper solder terminals.
I like to order cable with at least one terminal already soldered on by the supplier. This is the terminal I put at the masthead, appropriately waterproofed with adhesive-lined heat shrink (my preference), amalgamating tape, or silicone sealant. I feed the bare end through the mast and the boat, soldering on the connector at the radio end. In this way, I have a high level of confidence in the masthead terminal, and one I attach is easily accessible in case I botch the job.
Over and over we meet fellow cruisers lamenting poor performance of their VHF radios. All it usually takes to avoid this fate are fat wires, fat coax, and soldered terminals.
